CODEWITHSUNDEEP
2d-gamescollision
Barbara PM
Barbara PM

Reputation: 512

How do I detect triangle and rectangle intersection?

I am developing an Android game and I would like to know how to detect the collision of a rectangle knowing its position (x and y), width and height and a triangle knowing x,y, width and height. Triangles are always right triangles as the result of dividing a rectangle through its diagonal so the (x,y) parameter will be a position in the hypotenuse, not the center of the triangle. Any help would be appreciated!

Upvotes: 3

Views: 8342

Answers (2)

Dov Grobgeld
Dov Grobgeld

Reputation: 4983

Have a look at the great polygon intersection library. There is a C++ version that you may be able to use on Android.

Another possibility is to rasterize an image of the rectangle and another image with the triangle and finally check pixel by pixel if there is any intersection between the two images.

Upvotes: 0

Barbara PM
Barbara PM

Reputation: 512

I´ve finally done this using the function intersect for two lines. Lines are defined with initial point (x,y) and final point (x,y)

// a1 is line1 start, a2 is line1 end, b1 is line2 start, b2 is line2 end
 static boolean intersects(Vector2 a1, Vector2 a2, Vector2 b1, Vector2 b2)
{
    Vector2 intersection = Vector2.Zero();

    Vector2 b = Vector2.Subtract(a2,a1);
    Vector2 d = Vector2.Subtract(b2,b1);
    float bDotDPerp = b.getX() * d.getY() - b.getY() * d.getX();

    // if b dot d == 0, it means the lines are parallel so have infinite intersection points
    if (bDotDPerp == 0)
        return false;

    Vector2 c = Vector2.Subtract(b1,a1);
    float t = (c.getX() * d.getY() - c.getY() * d.getX()) / bDotDPerp;
    if (t < 0 || t > 1)
        return false;

    float u = (c.getX() * b.getY() - c.getY() * b.getX()) / bDotDPerp;
    if (u < 0 || u > 1)
        return false;

    intersection = Vector2.Sum(a1,Vector2.Multiply(b,t));

    return true;
}

To know if a triagle intersects a rectangle you check the intersection of every line from the triangle with every line from the rectangle with function above.

Upvotes: 6

Related Questions